1. Field
Methods and apparatuses consistent with exemplary embodiments relate to a data structure at the physical layer, and more particularly, to a data structure for future generation digital broadcasting systems, for example systems developed by the Digital Video Broadcasting (DVB) Project and/or the Advanced Television Systems Committee (ATSC) (e.g. the ATSC 3.0 Standard).
2. Description of the Related Art
Digital broadcasting techniques allow various types of digital content, for example video and audio data, to be distributed to end users. A number of standards have been developed for this purpose, including a family of standards developed by the ATSC organization, including ATSC 1.0 and ATSC 2.0 standards. The ATSC Digital Television (DTV) Standard, described in various documents, including A/52 and A/53, available at http://www.atsc.org, have been adopted for use in terrestrial broadcasting by various countries, including the United States, Canada and South Korea.
Recently, ATSC has begun developing a new standard, known as ATSC 3.0, for a delivery method of real-time and non-real-time television content and data to fixed and mobile devices. As part of this development, ATSC has published a Call for Proposals (CFP) document (TG3-S2 Doc. #023r20, “Call for Proposals For ATSC-3.0 PHYSICAL LAYER, A Terrestrial Broadcast Standard”, ATSC Technology Group 3 (ATSC 3.0), 26 Mar. 2013), in which a stated goal is to identify technologies that could be combined to create a new physical layer of an ATSC 3.0 Standard. It is envisaged that the ATSC 3.0 system will be designed with a layered architecture and a generalized layering model for ATSC 3.0 has been proposed. The scope of the aforementioned CFP is limited to the base layer of this model, the ATSC 3.0 Physical Layer, which corresponds to Layer 1 and 2 of the ISO/IEC 7498-1 model.
It is intended that ATSC 3.0 will not require backward compatibility with current broadcasting systems, including ATSC 1.0 and ATSC 2.0. However, the CFP states that, wherever practicable, the standard shall utilize and reference existing standards that are found to be effective solutions to meet the requirements.
Other existing standards developed for broadcasting digital content include a family of open standards developed and maintained by the Digital Video Broadcasting (DVB) Project and published by the European Telecommunications Standards Institute (ETSI). One such standard is DVB-T2, which is described in various documents, including ETSI EN 302 755 V1.3.1, (“Digital Video Broadcasting (DVB); Frame structure channel coding and modulation for a second generation digital terrestrial television broadcasting system (DVB-T2)”), and Technical Specification ETSI TS 102 831 V1.2.1 (“Digital Video Broadcasting (DVB); Implementation guidelines for a second generation digital terrestrial television broadcasting system (DVB-T2)”).
In DVB-T2, data is transmitted in a frame structure. Service data (for example in the form of one or more MPEG-2 Transport Streams, or Generic Encapsulated Streams (GSE)) may be separated into one or more data streams, which are then carried in the form of Physical Layer Pipes (PLPs). Each PLP is a logical channel, which may carry one or multiple services at a given Quality of Service (QoS). Each PLP is associated with a certain modulation and Forward Error Correction (FEC) protection mode which is statically configurable, and other Physical Layer (L1) configurations, for example time interleaving depth. A PLP is a container of baseband frames (BBFRAMEs) with a corresponding structure, and a BBFRAME cannot be owned by more than one PLP. A BBFRAME is an L1 container for encapsulating User Packets (UPs) received from the Data Link Layer (L2), and has a particular data structure that is processed independently by the FEC encoder. A BBFRAME may be regarded as a codeword structure.
FIG. 1 illustrates the structure of a DVB-T2 BBFRAME. The BBFRAME 100 comprises a header 101 of fixed length (10 bytes), a data field 103 of variable length (DFL), and a field 105 of variable length (PADL) for padding and/or in-band signalling. The total length of the BBFRAME 100 is fixed at Kbch bits.
The BBFRAME 100 is encoded by performing BCH outer coding and LDPC inner coding, and the parity check bits of the BCH outer code and the parity check bits of the inner LDPC code are appended to the end of the BBFRAME 100. The maximum size of the data field 103 DFL depends on the chosen LDPC code, the chosen BCH code, and whether or not the BBFRAME 100 includes in-band signalling.
The bits of UPs may be allocated to the data field of BBFRAMEs using fragmentation or no fragmentation. When using no fragmentation, an integer number of UPs are allocated to the data field 103 of each BBFRAME 100. When using fragmentation, a number of bits equal to the available data field capacity are allocated, thus potentially breaking up a UP across data fields 103 of subsequent BBFRAMEs 100.
The BBFRAME header 101 is inserted in front of the data field 103 and describes the format of the data field 105. The header 101 comprises a number of fields including a MATYPE field, an optional ISSY field, and a SYNCD field. The MATYPE field signals, among other things, the input stream format (e.g. TS or GSE). The SYNCD field indicates the distance in bits from the beginning of the data field 103 to the beginning of the first transmitted UP which starts in the data field 103. Data processing in the DVB-T2 modulator may produce variable transmission delay on the user information, and thus, the ISSY field carries information including the value of a counter clocked at the modulator clock rate, which can be used by a receiver to regenerate the correct timing of the regenerated output stream. The ISSY field carries other information, for example, related to the buffer size required at the receiver to decode the given PLP.
Padding 105 may be applied in circumstances when user data available for transmission is not sufficient to completely fill a BBFRAME 100, or when an integer number of UPs has to be allocated in a BBFRAME 100 (i.e. when no fragmentation is used). The padding field 105 may also be used to carry in-band signalling. The padding field 105 is appended after the data field 103 and has a size such that the BBFRAME 100 has a constant length of Kbch bits.
Another standard for digital broadcasting developed and maintained by the DVB Project is DVB-NGH, which is described in various documents including ETSI EN 303 105 V1.1.1 (“Digital Video Broadcasting (DVB); Next Generation broadcasting system to Handheld physical layer specification (DVB-NGH)”) and DVB Bluebook A160. DVB-NGH is designed for broadcasting digital content to handheld terminals, for example mobile telephones.
DVB-NGH keeps the same BBFRAME structure as DVB-T2 and also includes the options of fragmentation and no fragmentation. However, DVB-NGH provides different modes of operation, each mode using a certain header length and data field structure.
What is desired is a data structure, for example a baseband frame structure for use in future generation digital broadcasting systems, for example systems developed by the Digital Video Broadcasting (DVB) Project and/or the Advanced Television Systems Committee (ATSC) (e.g. the ATSC 3.0 Standard).
It is preferable, but not necessary, that the data structure has a good overhead efficiency, for example, such that the sizes of the header and padding field are relatively small compared to the size of the data field. It is also preferable, but not necessary, that the data structure is relatively simple to reduce the implementation complexity. It is also preferable, but not necessary, that the data structure has the capacity to be extended with relatively minor modifications, to enable the frame structure to incorporate new features and co-exist with both legacy and future standards.